First of all, what you "require" and what you get might differ from what you want to see since all answers here are given freely on a volunteer basis.

My answer is you are comparing apples and oranges. Many of your potential visitors will access Social Media platforms, as well as search engines, through their phones. So if you want to see an optimal number of visits to your site, you will need to do both unless you can linearize the content of your site so it will fit in mobile devices without express development for mobile.

Whether or not you develop for mobile, you should still develop a Social Media presence that is targeted for your demographic.

Which one do you think is more important for businesses - Mobile Optimization or Social Media Marketing?

Require inputs on this with relevant reasons.

I would say social media marketing as this will bring traffic to the site.Mobile optimization ... first maybe the business doesn't need mobile ( it's not specified ). Also considering that phones become bigger and bigger ... normal site will fit just perfectly in no time with no adjustment for the mobile.

Both have there different users and market. Mobile optimization has been increase recently because of increasing in mobile users and internet uses. Social media marketing is used to get aware people about your new services or products.

well.. it depends on your needs.. what kind of a business are you in and what are you looking forward to from mobile optimization and social media marketing..mobile optimization may not be useful for all the niches and all the businesses; social media marketting would work the best for all the niches and would bring in a lot of traffic=>promotion=>publicity=> more successful than mobile optimization.

It depends on what youre selling, if the potential customers will use the phones to enter your site, then mobile optimization comes first. But people who use phones to access websites, also use Social networks, so youll have to do both in the end.

I would suggest Social Media Marketing since most of the people are engage in this trend plus admit it or not, it becomes a medium of reaching out more people whether for personal means or business related activity.

This question is effectively comparing apples and oranges or really fruit and furniture. Both are pretty important to having a traditional meal and neither effects the existence of the other.

Certainly we are all constrained by resources but there's no reason you can't parallel or task jump doing some level of social while building a starting point in mobile [or more ideally making the existing site adapt to mobile use].

Smartphones are become ubiquitous, social is how people communicate information. Neither replaces or mitigates the value of the other so unless you have a specific problem [i.e. a very mobile focused customer base or an extremely socially designed product] it makes no sense to rationalize tabling one to pursue the other with more rigor.

According to me, I would suggest you both rather then concentrating on any one part. Mobile optimization is gaining more popularity day by day due to increase in number of smart phones. But Social media marketing is also a good source from were you can get potential attention of people.

For me, you should considered both field. Mobile marketing have a huge success now and for the future of marketing. Just like a growing number using their cellphone with doing social media and buying products online.